Move all core EE load balancing code to CE

This moves all files from:

ee/lib/gitlab/database/load_balancing* -> lib/gitlab/database
ee/spec/lib/gitlab/database/load_balancing* -> spec/lib/gitlab/database

config/initializers/load_balancing.rb

@@ -2,8 +2,7 @@
 
 # We need to run this initializer after migrations are done so it doesn't fail on CI
 
-Gitlab.ee do
-  if Gitlab::Database.cached_table_exists?('licenses')
+if Gitlab::Database.cached_table_exists?('licenses')
   if Gitlab::Database::LoadBalancing.enable?
     Gitlab::Database.disable_prepared_statements
 
@@ -21,5 +20,4 @@ Gitlab.ee do
     end
 
   end
-  end
 end

ee/spec/lib/gitlab/database/load_balancing/srv_resolver_spec.rb → spec/lib/gitlab/database/load_balancing/srv_resolver_spec.rb

@@ -52,7 +52,7 @@ RSpec.describe Gitlab::Database::LoadBalancing::SrvResolver do
   end
 
   def dns_response_packet_from_fixture(fixture_name)
-    fixture         = File.read(Rails.root + "ee/spec/fixtures/dns/#{fixture_name}.json")
+    fixture         = File.read(Rails.root + "spec/fixtures/dns/#{fixture_name}.json")
     encoded_payload = Gitlab::Json.parse(fixture)['payload']
     payload         = Base64.decode64(encoded_payload)